Organopolysiloxane compositions which cure by means of an addition reaction of alkenyl groups bonded to silicon atoms and hydrogen atoms bonded to silicon atoms are wellknown in the prior art. These compositions cure in a very short time by the action of heat. Not only is this property useful where operations have to be carried out continuously, but also, the reactions involved are not accompanied by the formation of by-products. In addition, there is little shrinkage in the curing process, and as the cured products have excellent heat resistance and electrical properties, they are widely used in potting and sealing of electrical and electronic components.
The polysiloxane compositions known in the prior art however do not adhere well to the substrate with which they are in contact when they cure. This property is desirable when they are used in mold-making applications, but it is a serious drawback where they are made to function as electrical insulators by means of potting, coating or sealing.
To improve their adhesion to the substrate, the surface of the substrate is often treated with primary coatings called a primer. As this primer contains an organic solvent, however, its use presents safety hazards, and it also increases the cost. Further, in the case of some substrate shapes and materials, it may be impossible to apply a primer.
Many attempts have already been made to make said organopolysiloxane compositions adhere to substrates when they cure without the use of a primer by adding various compounds to them.
Examples of such proposals include the addition of polysiloxanes with hydrogen atoms bonded to silicon atoms and trialkoxysilylalkyl groups (Japanese Patent KOKAI No. 48-16952, herein "Japanese Patent KOKAI" means Publication of Unexamined Japanese Patent), and the addition of polysiloxanes with epoxy groups and/or ester groups bonded to silicon atoms via carbon atoms bonded directly to silicon atoms, and hydrogen atoms bonded to silicon atoms (Japanese Patent KOKAI No. 50-39435), and the addition of polysiloxanes with epoxy group and trialkoxysilyl groups bonded to silicon atoms via carbon atoms bonded directly to silicon atoms, and hydrogen atoms bonded to silicon atoms (Japanese Patent KOKAI No. 53-33256), as a 3rd constituent.
In all of the above cases, however, the added component had insufficient wettability on the substrate, its adhesive functional groups such as epoxy and trialkoxysilyl groups did not function effectively, and it had poor self-adhesion properties on the various substrates used as electrical and electronic components.
The authors of the present invention carried out intensive studies to resolve the disadvantages of the prior art, and especially of these additives. We then found that by adding a silicon compound with fluoroalkyl groups or fluoroalkylether groups as a 3rd constituent to the polysiloxane composition which cures by reaction of hydrosilyl groups and alkenyl groups bonded to silicon atoms, and heating to a relatively low temperature for a short time, it was possible to make the composition adhere satisfactorily to metals and plastics.